The present invention relates generally to methods for use in disk drives for computer systems. More particularly, the present invention relates to methods for improving servo seek settling performance by selectively boosting the servo loop bandwidth during settling.
FIG. 1 is a diagrammatic representation of a conventional disk drive for use in a host computer system. Disk drive 10 includes at least one rotating rigid disk 14 mounted on a rotating hub 16. The hub 16 is typically secured to a spindle shaft (not shown) that is rotatably mounted to a bearing assembly and driven by a spindle motor. Disk drive 10 also includes an actuator assembly 20 mounted to the baseplate 11. Included in the actuator assembly 20 is a motor assembly 25 (e.g. voice coil motor) that produces a current profile induced torque for pivotably actuating a head actuator 21 about pivot 24 to position a read/write transducer head 19 back and forth between specific tracks 31, 32 concentrically defined on the disk 14. Although not shown it should be understood that actuator assembly 20 may include a plurality of integrated head actuators and read/write transducers to access a plurality of disks.
Each disk 14 includes a plurality of concentric tracks defined thereon for storing data. In addition, each disk 14 may also contain multiple spokes containing servo information that is useful with a head positioner servo system. Head positioner servo systems for disk drives are well known. Disk drive head positioner servos provide essentially two functions: track seeking or accessing, and track following. Ideally, a track seeking servo configuration moves the read/write head between two tracks in the minimum possible time, while track following servo configuration maintains the head at the centerline of a track being followed. These two quite different functions require different control circuit configuration for practical implementation, even though the same actuator structure, actuator driver circuit and mechanical system components are used for both tasks.
A third transitional mode, known as track settle, covers the situation where the track seeking servo has completed its task, and the servo circuitry has switched to the track following configuration, but the head transducer has yet stabilized at the target track location. Since read and write operations cannot be accomplished until the head has stabilized at the target track location, it is most desirable to minimize settle time.
With advancements in disk drive performance, seek times have decreased to approximately 7 msecs. As a result, higher torque levels are also required to effectively move the head positioners to meet the faster access time. A typical current profile 260 for creating such a torque, illustrated in FIG. 2, has a substantially exponential shape, after an initial sudden change of slope. The ruggedness of beginning section 264 signifies an abrupt change in the motor input current which commonly initiates vibration of the disk drive in addition to the desired actuator movement. A xe2x80x9cpolarity reversalxe2x80x9d section 268 of input current profile 260 signifies a transition from acceleration to deceleration. An ending section 272 signifies a final deceleration which causes the actuator to decelerate and eventually return to rest. The deceleration during ending section 272 represents the settling of the read/write head as it approaches the target location. The settling profile on approaching the target location typically entails some sort of ringing induced by an interaction between the drive and the environment. Depending on the drive mounting scheme, the disk drive 10 may also be susceptible to recoil disturbances as a result of the high torque levels generated by the actuator motor. Such recoil forces tend to prevent the read/write head from initially reaching the target location, thereby adversely lengthening the settle time, as illustrated in the FIG. 3 graphical representation. As shown, curve 120 represents the settling time T1, when disk drive is not subjected to recoil. When subjected to recoil, curve 110 never reaches the target location A, at time T1. In fact the recoil will tend to xe2x80x9cpushxe2x80x9d the actuator away from the target location A before finally settling at time T2. Traditionally, the solution to compensate for this recoil was to increase the bandwidth for both the servo settling controller as well as the track following controller. However, mechanical resonance of the head positioners (actuator arms) limit the flexibility to increase servo bandwidth. Another alternative to reducing recoil disturbance was to slow the seek operation. However, this may not be a viable alternative in high TPI and high seek performance disk drive systems where an aggressive seek profile is necessary.
Therefore, there exists a need for a method of improving the settling time to overcome the adverse effects of disk drive recoil during seek operation.
The present invention satisfies this need.
A general object of the present invention is to improve seek settling performance by selectively activating a momentary gain to servo loop bandwidth during settling.
More specifically, a gain enhancement control signal is selectively activated and combined with a closed loop control signal to provide a momentary boost to servo loop bandwidth when two conditions are satisfied during seek settling.
Another object of the present invention is to provide a disk drive having a controller that urges a read read/write transducer head from an initial location on a disk to a target location and selectively activates an enhanced control signal to further urge the read/write transducer head towards the target location.
In one aspect of the present invention, an absolute position value and a velocity of the read/write head are monitored as the read/write transducer head approaches the target location during a seek. When either the velocity approaches zero or the absolute position value changes signs, a gain enhanced control signal is activated to be combined with the closed loop control signal, and sent to an actuator amplifier to further urge the read/write transducer head towards the target location.
In another aspect of the present invention, the momentary gain activated to produce the gain enhanced control signal decays exponentially so as not to excite mechanical resonance within the drive.
These and other advantages of the present invention will become apparent upon reading the following detailed descriptions and studying the various figures of the drawings.